linux-kernel - Re: [RFC] PCI: fu740: Force Gen1 to fix initial device probing on some boards

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Message-ID: <10794ea9-95ff-2cde-5851-b757a73b00ee@codethink.co.uk>
Date:   Tue, 8 Mar 2022 09:45:36 +0000
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     helgaas@...nel.org, linux-pci@...r.kernel.org
Cc:     paul.walmsley@...ive.com, greentime.hu@...ive.com,
        lorenzo.pieralisi@....com, robh@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] PCI: fu740: Force Gen1 to fix initial device probing on
 some boards

On 28/02/2022 23:22, Ben Dooks wrote:
> The fu740 PCIe core does not probe any devices on the SiFive Unmatched
> board without this fix (or having U-Boot explicitly start the PCIe via
> either boot-script or user command). The fix is to start the link at
> Gen1 speeds and once the link is up then change the speed back.
> 
> The U-Boot driver claims to set the link-speed to Gen1 to get the probe
> to work (and U-Boot does print link up at Gen1) in the following code:
> https://source.denx.de/u-boot/u-boot/-/blob/master/drivers/pci/pcie_dw_sifive.c?id=v2022.01#L271
> 
> Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
> --
> Note, this patch has had significant re-work since the previous 4
> sets, including trying to fix style, message, reliance on the U-Boot
> fix and the comments about usage of LINK_CAP and reserved fields.

The internal feedback is this version is passing on our CI.

If there are no comments on this soon, I will post this as either the
v5 of the original or as a new patch.

> ---
>   drivers/pci/controller/dwc/pcie-fu740.c | 51 ++++++++++++++++++++++++-
>   1 file changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-fu740.c b/drivers/pci/controller/dwc/pcie-fu740.c
> index 842b7202b96e..16ad52f53490 100644
> --- a/drivers/pci/controller/dwc/pcie-fu740.c
> +++ b/drivers/pci/controller/dwc/pcie-fu740.c
> @@ -181,10 +181,59 @@ static int fu740_pcie_start_link(struct dw_pcie *pci)
>   {
>   	struct device *dev = pci->dev;
>   	struct fu740_pcie *afp = dev_get_drvdata(dev);
> +	u8 cap_exp = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +	int ret;
> +	u32 orig, tmp;
> +
> +	/*
> +	 * Force Gen1 when starting link, due to some devices not
> +	 * probing at higher speeds. This happens with the PCIe switch
> +	 * on the Unmatched board. The fix in U-Boot is to force Gen1
> +	 * and hope later resets will clear this capaility.
> +	 */
> +
> +	dev_dbg(dev, "cap_exp at %x\n", cap_exp);
> +	dw_pcie_dbi_ro_wr_en(pci);
> +
> +	tmp = dw_pcie_readl_dbi(pci, cap_exp + PCI_EXP_LNKCAP);
> +	orig = tmp & PCI_EXP_LNKCAP_SLS;
> +	tmp &= ~PCI_EXP_LNKCAP_SLS;
> +	tmp |= PCI_EXP_LNKCAP_SLS_2_5GB;
> +	dw_pcie_writel_dbi(pci, cap_exp + PCI_EXP_LNKCAP, tmp);
>   
>   	/* Enable LTSSM */
>   	writel_relaxed(0x1, afp->mgmt_base + PCIEX8MGMT_APP_LTSSM_ENABLE);
> -	return 0;
> +
> +	ret = dw_pcie_wait_for_link(pci);
> +	if (ret) {
> +		dev_err(dev, "error: link did not start\n");
> +		goto err;
> +	}
> +
> +	tmp = dw_pcie_readl_dbi(pci, cap_exp + PCI_EXP_LNKCAP);
> +	if ((tmp & PCI_EXP_LNKCAP_SLS) != orig) {
> +		dev_dbg(dev, "changing speed back to original\n");
> +
> +		tmp &= ~PCI_EXP_LNKCAP_SLS;
> +		tmp |= orig;
> +		dw_pcie_writel_dbi(pci, cap_exp + PCI_EXP_LNKCAP, tmp);
> +
> +		tmp = dw_pcie_readl_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL);
> +		tmp |= PORT_LOGIC_SPEED_CHANGE;
> +		dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, tmp);
> +
> +		ret = dw_pcie_wait_for_link(pci);
> +		if (ret) {
> +			dev_err(dev, "error: link did not start at new speed\n");
> +			goto err;
> +		}
> +	}
> +
> +	ret = 0;
> +err:
> +	// todo - if we do have an unliekly error, what do we do here?
> +	dw_pcie_dbi_ro_wr_dis(pci);
> +	return ret;
>   }
>   
>   static int fu740_pcie_host_init(struct pcie_port *pp)


-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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